JP5461886B2 - Optical path switching device, optical path switching method, and optical path switching program - Google Patents

Description

  The present invention relates to an optical path switching device, an optical path switching method, and an optical path switching program. The present invention particularly relates to an optical path switching device, an optical path switching method, and an optical path switching program suitable for switching an optical path between two transmission paths, a working transmission path and a backup transmission path, in a CATV optical transmission system.

  A CATV (Cable television) optical transmission system transmits data used for services such as television broadcasting and Internet browsing using an optical cable. In an optical transmission system typified by such a CATV optical transmission system, a technique for avoiding a failure by using two transmission lines, an active transmission line and a backup transmission line, is generally employed.

  A general method of this method is to detect when a working transmission line is disconnected due to a failure and switch to a backup transmission line. However, when this conventional method is adopted, when the optical device or the optical fiber itself constituting the working transmission line of the optical transmission system causes deterioration of characteristics due to aging, the transmission line can be switched only by the change of the state. Not done. This causes a problem that the reliability of the entire optical path network is lowered.

  Therefore, a technical idea that can cope with degradation of one of the transmission lines when using two transmission lines, a working transmission line and a standby transmission line, has been proposed as a related technique of the present invention (see, for example, Patent Document 1). ).

  FIG. 14 is a diagram for explaining a related technique of the present invention that solves a problem when a transmission path is deteriorated in an optical transmission system. The proposed optical path switching apparatus 100 inputs the working transmission line 101 and the standby transmission line 102 to the optical output signal switching unit 103, and outputs the switched optical signal to the output transmission line 104. Yes.

  In the optical path switching device 100, a working light level detection unit 105 connected to the working transmission line 101 and a protection light level detection unit 106 connected to the protection transmission line 102 are provided. The level of the optical signal on the road is detected. The detection results 107 and 108 of the working light level detection unit 105 and the backup light level detection unit 106 are input to the light level identification unit 109 and compared with a predetermined threshold value. As a result, when it is determined that the detection level of only the detection result 107 of the working transmission line 101 is equal to or less than the threshold value, the optical level identification unit 109 sends a switching request signal 111 to the optical output signal switching unit 103. When the optical output signal switching unit 103 receives this switching request signal 111, the optical output signal switching unit 103 switches the transmission path from the active transmission path 101 to the backup transmission path 102. Of course, even when the working transmission line 101 is disconnected, switching from the working transmission line 101 to the backup transmission line 102 is performed, and it becomes possible to avoid a failure in the optical path network.

JP-A-10-303814 (paragraphs 0023 to 0025, FIG. 1)

  By the way, in an optical path network, an optical signal transmitted through the optical path network is converted from an electrical signal and transmitted. Therefore, the degradation of the optical transmission line is also a problem, but the signal level is reduced due to the deterioration of the element used in the electric signal processing stage and the change in the attenuation of the electric signal due to the ambient temperature, There is also a problem that the noise level deteriorates. Without detecting such a malfunction in the signal state at the stage of the electrical signal that is the source of transmission, only the level reduction that occurred during the transmission process of the optical signal after converting it from an electrical signal to an optical signal and amplifying it if necessary It is not possible to improve the reliability of the entire optical path network only by dealing with the above.

  Accordingly, an object of the present invention is to detect an optical signal failure before being converted to an optical signal and sent to an optical transmission line, and to switch an optical path network, an optical path switching method, an optical path switching method, and an optical It is to provide a path switching program.

  In the present invention, (a) a working optical transmission line sending means for mixing a signal to be transmitted and a working pilot signal at a level serving as a reference for a specific wavelength region, and sending them to the working optical transmission line; A standby optical transmission line sending means for mixing the transmission target signal and a standby pilot signal at a level serving as a reference for a specific wavelength region and sending the mixed signal to the spare optical transmission line; and (c) the above-described active optical transmission. A working pilot signal extracting means for extracting the above-described working pilot signal from the working transmission line that has passed through the path sending means; and Pilot signal extracting means; (e) working pilot signal voltage converting means for converting the working pilot signal extracted by the above-described working pilot signal extracting means into voltage; A preliminary pilot signal voltage converting means for converting the preliminary pilot signal extracted by the pilot signal extracting means into a voltage; and (g) a working pilot voltage converted by the above-described working pilot signal voltage converting means and the above-described spare pilot signal voltage converting means. A comparison means for comparing the converted spare pilot voltage with a predetermined threshold voltage; and (h) one transmission line out of the working optical transmission line and the spare optical transmission line described above according to the comparison result of the comparison means. The optical path switching device includes an optical path selection unit that selects a transmission path on the output side.

  In the present invention, (a) a working optical transmission line sending means for mixing a signal to be transmitted and a working pilot signal at a level serving as a reference for a specific wavelength region, and sending the mixed signal to the working optical transmission line; (B) standby optical transmission line transmission means for mixing the transmission target signal and a preliminary pilot signal at a level serving as a reference for a specific wavelength region, and transmitting the mixed signal to a standby optical transmission line; A working pilot signal extracting means for extracting the above-described working pilot signal from the working transmission line that has passed through the optical transmission line sending means; and And (e) working pilot signal voltage converting means for converting the working pilot signal extracted by the working pilot signal extracting means into a voltage; A spare pilot signal voltage converting means for converting the spare pilot signal extracted by the spare pilot signal extracting means to a voltage; and (g) a position closer to the working pilot signal than the working pilot signal from the working transmission path through the working optical transmission line sending means. A working noise signal extracting means for extracting a noise signal in a wavelength band whose frequency is shifted by a fixed amount; and (h) a frequency of a predetermined amount from the backup pilot signal through the backup optical path transmission means described above than the backup pilot signal. Preliminary noise signal extracting means for extracting a noise signal in a shifted wavelength band; (i) a working noise signal voltage converting means for converting the working noise signal extracted by the working noise signal extracting means to a voltage; Preliminary noise signal voltage converting means for converting the preliminary noise signal extracted by the preliminary noise signal extracting means into voltage, and Working CN detecting means for detecting a C / N (Carrier to Noise Ratio) using the working pilot voltage converted by the pilot signal voltage converting means and the working noise voltage converted by the working noise signal voltage converting means; ) A preliminary CN detection means for detecting C / N using the preliminary pilot voltage converted by the preliminary pilot signal voltage conversion means and the preliminary noise voltage converted by the preliminary noise signal voltage conversion means; Comparison means for comparing the current CN level detected by the current CN detection means and the preliminary CN level detected by the preliminary CN detection means with a predetermined threshold voltage, and (f) the comparison result of this comparison means. In response, an optical path selecting means for selecting one transmission line as an output side transmission line from the above-described active optical transmission line and backup optical transmission line Scan switching device is provided.

  Furthermore, in the present invention, (a) a working pilot signal for extracting the above-described working pilot signal from a working transmission line that mixes and transmits a signal to be transmitted and a working pilot signal at a reference level in a specific wavelength region. An extraction step; (b) a spare pilot signal for extracting the spare pilot signal from a spare transmission line that mixes and transmits the signal to be transmitted and a spare pilot signal at a reference level in a specific wavelength region; An extraction step; (c) a working pilot signal voltage conversion step for converting the working pilot signal extracted in the above-described working pilot signal extraction step into a voltage; and (d) a preliminary pilot signal extracted in the above-described preliminary pilot signal extraction step. A preliminary pilot signal voltage converting step for converting to a voltage, and (e) the above-described working pilot A comparison step for comparing the current pilot voltage converted in the signal voltage conversion step and the preliminary pilot voltage converted in the preliminary pilot signal voltage conversion step with a predetermined threshold voltage; Accordingly, the optical path switching method includes an optical path selection step of selecting one transmission path as an output side transmission path from the above-described active optical transmission path and backup optical transmission path.

  Furthermore, in the present invention, (a) a working pilot that extracts the above-described working pilot signal from a working transmission line that mixes and transmits a signal to be transmitted and a working pilot signal at a reference level in a specific wavelength region. A signal extraction step; and (b) a spare pilot for extracting the spare pilot signal from a spare transmission line that mixes and transmits the signal to be transmitted and a spare pilot signal at a reference level in a specific wavelength region. A signal extracting step; (c) a working pilot signal voltage converting step for converting the working pilot signal extracted in the above-described working pilot signal extracting step into a voltage; and (d) a spare pilot signal extracted in the above-described preliminary pilot signal extracting step. A preliminary pilot signal voltage converting step for converting the voltage into a voltage, and (e) the above-described active optical transmission An active noise signal extracting step for extracting a noise signal in a wavelength band whose frequency is shifted by a predetermined amount from the above-described active pilot signal, and (f) a predetermined amount from the above-mentioned backup optical transmission line by a predetermined amount from the above-mentioned backup pilot transmission line. A preliminary noise signal extraction step for extracting a noise signal in a wavelength band whose frequency is shifted; (g) a working noise signal voltage conversion step for converting the working noise signal extracted in the above-described working noise signal extraction step into a voltage; ) A preliminary noise signal voltage conversion step for converting the preliminary noise signal extracted in the preliminary noise signal extraction step into a voltage; and (i) a current pilot voltage converted in the above-described current pilot signal voltage conversion step and the current noise signal described above. Current C / N is detected using the working noise voltage converted in the voltage conversion step. CN detection step and (nu) a preliminary CN detection step for detecting C / N using the preliminary pilot voltage converted in the preliminary pilot signal voltage conversion step and the preliminary noise voltage converted in the preliminary noise signal voltage conversion step. And (le) a comparison step for comparing the current CN level detected in the above-mentioned current CN detection step and the backup CN level detected in the above-mentioned backup CN detection step with a predetermined threshold voltage; The optical path switching method includes an optical path selection step of selecting one transmission line as an output side transmission line from the above-described active optical transmission line and backup optical transmission line according to the comparison result of the comparison step.

  Further, in the present invention, the optical path switching program is as described above from (i) the working transmission line that mixes and transmits the signal to be transmitted and the working pilot signal at the level serving as the reference for the specific wavelength region. The working pilot signal extraction process for extracting the working pilot signal, and (b) the spare transmission path for mixing and transmitting the signal to be transmitted and the spare pilot signal at the level serving as the reference for the specific wavelength region are described above. A preliminary pilot signal extracting process for extracting a preliminary pilot signal; (c) a working pilot signal voltage converting process for converting the working pilot signal extracted by the above-described working pilot signal extracting process into a voltage; and (d) the above-described spare pilot signal. Preliminary pilot signal voltage conversion processing for converting the preliminary pilot signal extracted by the extraction processing into voltage, and (e) before A comparison process for comparing the current pilot voltage converted by the current pilot signal voltage conversion process and the preliminary pilot voltage converted by the preliminary pilot signal voltage conversion process with a predetermined threshold voltage; According to the comparison result, the optical path selection process for selecting one transmission line as an output side transmission line from the working optical transmission line and the backup optical transmission line is executed.

  Further, in the present invention, the optical path switching program is as described above from (i) the working transmission line that mixes and transmits the signal to be transmitted and the working pilot signal at the level serving as the reference for the specific wavelength region. The working pilot signal extraction process for extracting the working pilot signal, and (b) the spare transmission path for mixing and transmitting the signal to be transmitted and the spare pilot signal at the level serving as the reference for the specific wavelength region are described above. A preliminary pilot signal extracting process for extracting a preliminary pilot signal; (c) a working pilot signal voltage converting process for converting the working pilot signal extracted by the above-described working pilot signal extracting process into a voltage; and (d) the above-described spare pilot signal. Preliminary pilot signal voltage conversion processing for converting the preliminary pilot signal extracted by the extraction processing into voltage, and (e) before A working noise signal extraction process for extracting a noise signal in a wavelength band whose frequency is shifted from the working pilot signal by a predetermined amount from the working optical transmission line, and (f) the spare pilot signal described above from the spare optical transmission line. A preliminary noise signal extraction process for extracting a noise signal in a wavelength band whose frequency is shifted by a predetermined amount, and (g) a working noise signal voltage conversion for converting the working noise signal extracted by the above-described working noise signal extraction process into a voltage. And (h) a preliminary noise signal voltage conversion process for converting the preliminary noise signal extracted in the preliminary noise signal extraction process to a voltage, and (i) a working pilot voltage converted by the above-described current pilot signal voltage conversion process, and A working CN detection process for detecting C / N using the working noise voltage converted by the working noise signal voltage conversion process described above; (N) a preliminary CN detection process for detecting C / N using the preliminary pilot voltage converted by the preliminary pilot signal voltage conversion process and the preliminary noise voltage converted by the preliminary noise signal voltage conversion process; A comparison process for comparing the current CN level detected in the above-described current CN detection process and the backup CN level detected in the above-mentioned backup CN detection process with a predetermined threshold voltage; Depending on the result, the optical path selection process is executed to select one transmission line as the output side transmission line from the working optical transmission line and the backup optical transmission line.

  As described above, according to the present invention, in an optical path network using two transmission lines, an active transmission line and a backup transmission line, the level of the pilot signal in the electrical signal before being converted into the optical signal is changed to the optical transmission line. The optical path is selected by comparing with a threshold value. Therefore, it is possible to prevent the occurrence of a failure of the optical signal in the optical path network due to the decrease in the level of the electrical signal before the transmission to the optical path network, and to improve the reliability of the entire optical path network.

  Further, in the present invention, in an optical path network using two transmission lines, a working transmission line and a backup transmission line, when the pilot signal and noise signal in the electrical signal before being converted into the optical signal have passed through the optical transmission line In this case, the CN level is detected and compared with a threshold value, and an optical path is selected. Therefore, even if the noise level of the optical path network is deteriorated, it is possible to prevent the reliability of the entire optical path network from being lowered.

It is a claim corresponding | compatible figure of the optical path switching apparatus of this invention. It is a claim corresponding | compatible figure of the other optical path switching apparatus of this invention. It is a claim corresponding figure of the optical path switching method of the present invention. It is a claim corresponding | compatible figure of the other optical path switching method of this invention. It is a claim corresponding | compatible figure of the optical path switching program of this invention. It is a claim corresponding | compatible figure of the other optical path switching program of this invention. 1 is a system configuration diagram showing a main part of an optical path network for CATV in a first embodiment of the present invention. It is a circuit diagram showing the structure of the optical path switching apparatus in 1st Embodiment. It is a block diagram showing the specific structure of the level identification part in 1st Embodiment. It is the flowchart which showed the flow of the process of the level identification part in 1st Embodiment. It is a circuit diagram showing the structure of the optical path switching apparatus in the 2nd Embodiment of this invention. It is a block diagram showing the specific structure of the CN level identification part in 2nd Embodiment. It is the flowchart which showed the flow of the process of the CN level identification part in 2nd Embodiment. It is a circuit diagram showing the optical path switching circuit and its periphery in the related art of the present invention.

  FIG. 1 is a diagram corresponding to the claims of the optical path switching apparatus according to the present invention. The optical path switching device 10 of the present invention includes a working optical transmission line sending means 11, a standby optical transmission line sending means 12, a working pilot signal extracting means 13, a spare pilot signal extracting means 14, a working pilot signal voltage converting means 15, a spare pilot. A signal voltage conversion unit 16, a comparison unit 17, and an optical path selection unit 18 are provided. Here, the working optical transmission line sending means 11 mixes the signal to be transmitted and the working pilot signal at a level that serves as a reference for a specific wavelength region and sends it to the working optical transmission line. The spare optical transmission line sending means 12 mixes the signal to be transmitted and the spare pilot signal at a level that serves as a reference for a specific wavelength region, and sends it to the spare optical transmission line. The working pilot signal extraction unit 13 extracts the above-described working pilot signal from the working transmission line that has passed through the working optical transmission line sending unit 11. The spare pilot signal extracting means 14 extracts the aforementioned spare pilot signal from the spare transmission line that has passed through the spare optical transmission line sending means 12. The working pilot signal voltage converting means 15 converts the working pilot signal extracted by the working pilot signal extracting means 13 into a voltage. The preliminary pilot signal voltage conversion means 16 converts the preliminary pilot signal extracted by the preliminary pilot signal extraction means 14 into a voltage. The comparing means 17 compares the working pilot voltage converted by the working pilot signal voltage converting means 15 and the spare pilot voltage converted by the spare pilot signal voltage converting means 16 with a predetermined threshold voltage. The optical path selection unit 18 selects one transmission line as the output side transmission line from the above-described working optical transmission line and backup optical transmission line according to the comparison result of the comparison unit 17.

  FIG. 2 shows a claim correspondence diagram of another optical path switching apparatus of the present invention. Another optical path switching apparatus 20 according to the present invention includes a working optical transmission line transmission means 21, a standby optical transmission line transmission means 22, a working pilot signal extraction means 23, a standby pilot signal extraction means 24, a working pilot signal voltage conversion means 25, Preliminary pilot signal voltage converting means 26, working noise signal extracting means 27, spare noise signal extracting means 28, working noise signal voltage converting means 29, spare noise signal voltage converting means 30, working CN detecting means 31, spare CN detecting means 32, Comparing means 33 and optical path selecting means 34 are provided. Here, the working optical transmission line sending means 21 mixes a signal to be transmitted and a working pilot signal at a level that becomes a reference in a specific wavelength region, and sends it to the working optical transmission line. The spare optical transmission line sending means 22 mixes the signal to be transmitted and the spare pilot signal at a level that serves as a reference for a specific wavelength region, and sends it to the spare optical transmission line. The working pilot signal extracting unit 23 extracts the above-described working pilot signal from the working transmission line that has passed through the working optical transmission line sending unit 21. The spare pilot signal extracting means 24 extracts the spare pilot signal described above from the spare transmission line that has passed through the spare optical transmission line sending means 22. The working pilot signal voltage converting means 25 converts the working pilot signal extracted by the working pilot signal extracting means 23 into a voltage. The preliminary pilot signal voltage conversion means 26 converts the preliminary pilot signal extracted by the preliminary pilot signal extraction means 24 into a voltage. The working noise signal extraction means 27 extracts a noise signal in a wavelength band whose frequency is shifted by a predetermined amount from the working pilot signal described above from the working transmission line that has passed through the working optical transmission line sending means 21. The spare noise signal extracting means 28 extracts a noise signal in a wavelength band whose frequency is shifted by a predetermined amount from the spare pilot signal described above from the spare transmission line that has passed through the spare optical transmission line sending means 22. The working noise signal voltage conversion means 29 converts the working noise signal extracted by the working noise signal extraction means 27 into a voltage. The preliminary noise signal voltage conversion means 30 converts the preliminary noise signal extracted by the preliminary noise signal extraction means 28 into a voltage. The working CN detecting means 31 detects C / N using the working pilot voltage converted by the working pilot signal voltage converting means 25 and the working noise voltage converted by the working noise signal voltage converting means 29. The backup CN detection means 32 detects C / N using the backup pilot voltage converted by the backup pilot signal voltage conversion means 26 and the backup noise voltage converted by the backup noise signal voltage conversion means 30. The comparison means 33 compares the current CN level detected by the current CN detection means 31 and the backup CN level detected by the backup CN detection means 32 with a predetermined threshold voltage. The optical path selection unit 34 selects one transmission line as the output side transmission line from the above-described active optical transmission line and backup optical transmission line according to the comparison result of the comparison unit 33.

  FIG. 3 is a diagram corresponding to claims of the optical path switching method of the present invention. The optical path switching method 40 of the present invention includes a working pilot signal extraction step 41, a backup pilot signal extraction step 42, a working pilot signal voltage conversion step 43, a backup pilot signal voltage conversion step 44, a comparison step 45, and an optical path selection step 46. I have. Here, in the working pilot signal extraction step 41, the above-described working pilot signal is extracted from the working transmission line that mixes and transmits the signal to be transmitted and the working pilot signal at the level serving as the reference for the specific wavelength region. In the spare pilot signal extraction step 42, the spare pilot signal is extracted from the spare transmission path for transmitting the signal to be transmitted and the spare pilot signal at a level serving as a reference for a specific wavelength region. In the working pilot signal voltage conversion step 43, the working pilot signal extracted in the working pilot signal extraction step 41 is converted into a voltage. In the preliminary pilot signal voltage conversion step 44, the preliminary pilot signal extracted in the preliminary pilot signal extraction step 42 is converted into a voltage. In the comparison step 45, the working pilot voltage converted in the working pilot signal voltage converting step 43 and the spare pilot voltage converted in the spare pilot signal voltage converting step 44 are compared with a predetermined threshold voltage. In the optical path selection step 46, one transmission line is selected as an output-side transmission line from the above-described active optical transmission line and backup optical transmission line according to the comparison result in the comparison step 45.

  FIG. 4 is a diagram corresponding to claims of another optical path switching method of the present invention. Another optical path switching method 50 of the present invention includes a working pilot signal extraction step 51, a spare pilot signal extraction step 52, a working pilot signal voltage conversion step 53, a spare pilot signal voltage conversion step 54, a working noise signal extraction step 55, a spare A noise signal extraction step 56, a working noise signal voltage conversion step 57, a spare noise signal voltage conversion step 58, a working CN detection step 59, a spare CN detection step 60, a comparison step 61, and an optical path selection step 62 are provided. Here, in the working pilot signal extraction step 51, the above-described working pilot signal is extracted from the working transmission line that mixes and transmits the signal to be transmitted and the working pilot signal at the level serving as the reference for the specific wavelength region. In the preliminary pilot signal extraction step 52, the preliminary pilot signal is extracted from the preliminary transmission path for mixing and transmitting the transmission target signal and the preliminary pilot signal at the level serving as the reference for the specific wavelength region. In the working pilot signal voltage conversion step 53, the working pilot signal extracted in the working pilot signal extraction step 51 is converted into a voltage. In the preliminary pilot signal voltage conversion step 54, the preliminary pilot signal extracted in the preliminary pilot signal extraction step 52 is converted into a voltage. In a working noise signal extraction step 55, a noise signal in a wavelength band whose frequency is shifted by a predetermined amount from the working pilot signal is extracted from the working optical transmission line. In a preliminary noise signal extraction step 56, a noise signal in a wavelength band having a frequency shifted by a predetermined amount from the preliminary pilot signal is extracted from the preliminary optical transmission line. In the working noise signal voltage conversion step 57, the working noise signal extracted in the working noise signal extraction step 55 is converted into a voltage. In the preliminary noise signal voltage conversion step 58, the preliminary noise signal extracted in the preliminary noise signal extraction step 56 is converted into a voltage. In the working CN detection step 59, C / N is detected using the working pilot voltage converted in the working pilot signal voltage conversion step 53 and the working noise voltage converted in the working noise signal voltage conversion step 54. In the preliminary CN detection step 60, C / N is detected using the preliminary pilot voltage converted in the preliminary pilot signal voltage conversion step 58 and the preliminary noise voltage converted in the preliminary noise signal voltage conversion step 58. In the comparison step 61, the current CN level detected in the current CN detection step 59 and the backup CN level detected in the backup CN detection step 60 are compared with a predetermined threshold voltage. In the optical path selection step 62, one transmission path is selected as the output transmission path from the above-described active optical transmission path and backup optical transmission path according to the comparison result of the comparison step 61.

  FIG. 5 shows a claim correspondence diagram of the optical path switching program of the present invention. The optical path switching program 70 according to the present invention is a computer that uses an active pilot signal extraction process 71, a spare pilot signal extraction process 72, an active pilot signal voltage conversion process 73, a spare pilot signal voltage conversion process 74, a comparison process 75, and an optical path selection. The process 76 is executed. Here, in the working pilot signal extraction processing 71, the above-described working pilot signal is extracted from the working transmission line that mixes and transmits the signal to be transmitted and the working pilot signal at the level serving as the reference for the specific wavelength region. In the spare pilot signal extraction process 72, the spare pilot signal is extracted from a spare transmission line that mixes and transmits a signal to be transmitted and a spare pilot signal at a reference level in a specific wavelength region. In the working pilot signal voltage conversion processing 73, the working pilot signal extracted by the working pilot signal extraction processing 71 is converted into a voltage. In the preliminary pilot signal voltage conversion processing 74, the preliminary pilot signal extracted in the preliminary pilot signal extraction processing 72 is converted into a voltage. In the comparison process 75, the working pilot voltage converted by the working pilot signal voltage conversion process 73 and the spare pilot voltage converted by the spare pilot signal voltage conversion process 74 are compared with a predetermined threshold voltage. In the optical path selection process 76, one transmission line is selected as the output transmission line from the above-described active optical transmission line and backup optical transmission line according to the comparison result of the comparison process 75.

  FIG. 6 shows a claim correspondence diagram of another optical path switching program of the present invention. Another optical path switching program 80 according to the present invention includes a computer, a working pilot signal extraction process 81, a spare pilot signal extraction process 82, a working pilot signal voltage conversion process 83, a spare pilot signal voltage conversion process 84, and a working noise signal extraction process. 85, preliminary noise signal extraction processing 86, active noise signal voltage conversion processing 87, preliminary noise signal voltage conversion processing 88, active CN detection processing 89, preliminary CN detection processing 90, comparison processing 91, and optical path selection processing 92 to be selected. I am trying to execute it. Here, in the working pilot signal extraction processing 81, the above-described working pilot signal is extracted from the working transmission line that mixes and transmits the signal to be transmitted and the working pilot signal at the level serving as the reference for the specific wavelength region. In the spare pilot signal extraction process 82, the spare pilot signal is extracted from a spare transmission line that mixes and transmits a signal to be transmitted and a spare pilot signal at a reference level in a specific wavelength region. In the working pilot signal voltage conversion process 83, the working pilot signal extracted in the working pilot signal extraction process 81 is converted into a voltage. In the preliminary pilot signal voltage conversion process 84, the preliminary pilot signal extracted in the preliminary pilot signal extraction process 82 is converted into a voltage. In the working noise signal extraction process 85, a noise signal in a wavelength band whose frequency is shifted by a predetermined amount from the working pilot signal is extracted from the working optical transmission line. In the spare noise signal extraction process 86, a noise signal in a wavelength band whose frequency is shifted from the spare optical transmission line by a predetermined amount from the spare pilot signal is extracted. In the working noise signal voltage conversion processing 87, the working noise signal extracted by the working noise signal extraction processing 85 is converted into a voltage. In the preliminary noise signal voltage conversion processing 88, the preliminary noise signal extracted by the preliminary noise signal extraction processing 86 is converted into a voltage. In the working CN detection processing 89, C / N is detected using the working pilot voltage converted by the working pilot signal voltage conversion processing 83 and the working noise voltage converted by the working noise signal voltage conversion processing 87. In the preliminary CN detection processing 90, C / N is detected using the preliminary pilot voltage converted by the preliminary pilot signal voltage conversion processing 84 and the preliminary noise voltage converted by the preliminary noise signal voltage conversion processing 88. In the comparison process 91, the current CN level detected in the current CN detection process 89 and the backup CN level detected in the backup CN detection process 90 are compared with a predetermined threshold voltage. In the optical path selection process 92, one transmission path is selected as an output transmission path from the above-described active optical transmission path and backup optical transmission path in accordance with the comparison result of the comparison process 91.

  <First Embodiment of the Invention>

  Next, a first embodiment of the present invention will be described.

  FIG. 7 shows the main part of the optical path network for CATV in the first embodiment of the present invention. In the optical path network 200, an active optical transmitter 202 for the active transmission line 201 and a standby optical transmitter 204 for the standby transmission line 203 are arranged. The working optical transmitter 202 receives an electrical signal as an output of the working mixer 207 that mixes the transmission outputs of the working CATV signal transmitter 205 and the working pilot signal transmitter 206. The spare optical transmitter 204 receives an electrical signal as an output of the spare mixer 211 that mixes the transmission outputs of the spare CATV signal transmitter 209 and the spare pilot signal transmitter 210.

  Here, the transmission output of the working CATV signal transmitter 205 and the backup CATV signal transmitter 209 is a CATV signal including electrical signals such as video, audio, and data signals. The transmission outputs of the working pilot signal transmitter 206 and the standby pilot signal transmitter 210 are signals of frequencies used outside the signal band used by the working CATV signal transmitter 205 and the standby CATV signal transmitter 209, and their levels are It is held at a constant value. The active mixer 207 and the premixer 211 mix the CATV signal and the pilot signal by wavelength multiplexing. Instead of performing wavelength multiplexing, a pilot signal may be output in a time zone in which the original CATV signal is not output, and both may be time division multiplexed.

  The working optical transmitter 202 converts the input electrical signal into an optical signal and outputs it. The optical signal output from the working optical transmitter 202 is input to one of the optical path switching devices 212 via the working transmission line 201. The standby optical transmitter 204 also converts the input electrical signal into an optical signal and outputs it. The optical signal output from the backup optical transmitter 204 is input to the other side of the optical path switching device 212 via the backup transmission path 203. The optical path switching device 212 selects one of the working transmission line 201 and the backup transmission line 203 and sends an optical signal to the transmission line 213 on the output side. The transmission line 213 on the output side is transmitted through the optical path network through an optical repeater amplifier (not shown).

FIG. 8 shows the configuration of the optical path switching device. In the optical path switching device 212 of this embodiment, an optical output signal switching unit 221 connected to the working transmission line 201 and the backup transmission line 203 is arranged. The transmission line from the working transmission line 201 to the optical output signal switching unit 221 is branched on the way, and has been transmitted to the end of the working transmission line branching transmission line 2011, which is _one of the branched transmission lines. A photoelectric conversion element 222 that photoelectrically converts an optical signal is disposed. The photoelectric conversion element 222, an optical element (not shown) for collecting light signal transmitted the working path branch transmission line 201 ₁ is disposed.

Similarly, the transmission path from the standby transmission path 203 to the optical output signal switching unit 221 is branched in the middle, and is transmitted to the end of the backup transmission path branch transmission path 2031, which is _one of the branched transmission paths. A photoelectric conversion element 223 for photoelectrically converting the obtained optical signal is disposed. The photoelectric conversion element 223 is also provided with an optical element (not shown) that collects the optical signal transmitted through the auxiliary transmission line branch transmission line 203 ₁ .

  The active-side photoelectric conversion element 222 is made of, for example, a photodiode, and has a cathode side connected to the power supply line 224 and an anode side grounded via a resistor 225. Therefore, when an optical signal enters the photoelectric conversion element 222 and its resistance changes, the potential at the connection point between the photoelectric conversion element 222 and the resistor 225 changes. This potential change is input to the working detection circuit 227 as a potential change signal 226.

  On the other hand, the photoelectric conversion element 223 on the standby side in the optical path switching device 212 is also made of, for example, a photodiode, the cathode side is connected to the power supply line 228, and the anode side is grounded via the resistor 229. Therefore, when an optical signal enters the photoelectric conversion element 223 and the resistance thereof changes, the potential at the connection point between the photoelectric conversion element 223 and the resistor 229 changes. This potential change is input to the preliminary detection circuit 232 as a potential change signal 231.

  The active detection circuit 227 and the preliminary detection circuit 232 are a kind of low-pass filter, and perform detection by inputting the potential change signals 226 and 231 when the pilot signal is input. Specifically, the current detection circuit 227 and the preliminary detection circuit 232 output voltage levels (hereinafter referred to as pilot signal levels) at the time of pilot signal input as detection signals 233 and 234, respectively.

  Detection signals 233 and 234 output from the current detection circuit 227 and the preliminary detection circuit 232 are input to the level identification unit 235. The level identifying unit 235 identifies the pilot signal levels of the detection signals 233 and 234, and outputs a switching request signal 236 to the optical output signal switching unit 221 in a predetermined case. When the switching request signal 236 is input, the optical output signal switching unit 221 switches between the working transmission line 201 and the standby transmission line 203 for the transmission line 213 on the output side.

  8 described above shows a part of the optical path network 200 shown in FIG. In the entire optical path network 200, as shown in the example of the optical path switching device 212, the working transmission line 201 and the backup transmission line 203 exist in pairs.

  FIG. 9 shows a specific configuration of the level identification unit. The level identification unit 235 includes a main control unit 243 including a CPU (Central Processing Unit) 241 and a memory 242 such as a ROM (Read Only Memory) storing a control program. The main control unit 243 is connected to the following units through signal transmission means such as a bus (not shown), and performs overall control thereof.

  The threshold value holding memory 244 holds the threshold value of the pilot signal included in the detection signals 233 and 234. The threshold is preset by the administrator of the optical path network 200 shown in FIG. The working pilot signal level storage unit 245 extracts the voltage level of the working pilot signal from the detection signal 233, and overwrites and stores the stored contents so far. The spare pilot signal level storage unit 246 extracts the voltage level of the spare pilot signal from the detection signal 234, and overwrites and stores the stored contents so far. Threshold comparison unit 247 compares the pilot signal voltage level sequentially stored in working pilot signal level storage unit 245 or backup pilot signal level storage unit 246 with the threshold value stored in threshold holding memory 244. To do. Switching request signal output unit 248 outputs switching request signal 236 when one of the voltage levels of the working pilot signal and the spare pilot signal is lower than the threshold value as a result of comparison by threshold comparing unit 247. When the voltage levels of both the active pilot signal and the spare pilot signal are lower than the threshold value, an error signal indicating the occurrence of an error may be output.

  FIG. 10 shows the processing flow of the level identification unit configured as described above. This will be described with reference to FIGS.

  The main control unit 243 waits for the inspection timing of the working transmission line 201 and the standby transmission line 203 at the locations shown in FIG. 7 in the optical path network 200 to arrive (step S301). The inspection timing may be generated every time a predetermined time elapses, or the inspection timing may be generated when requested by an administrator of the optical path network 200.

  When the inspection timing of the working transmission line 201 and the backup transmission line 203 comes (step S301: Y), the level identifying unit 235 reads the latest working pilot signal level stored in the working pilot signal level storage unit 245 ( In step S302, the magnitude of the voltage is compared with the threshold value held in the threshold value holding memory 244 (step S303). As a result, if the level of the latest working pilot signal is not less than the threshold value (N), the level of the latest spare pilot signal stored in the spare pilot signal level storage unit 246 is read (step S304). Then, the voltage level is compared with the threshold value held in the threshold value holding memory 244 (step S305). As a result, if the level of the latest spare pilot signal is not less than the threshold (N), not only the levels of the working pilot signal and the spare pilot signal but also the pair of working transmission line 201 and spare transmission line 203 It turns out that both are normal. Therefore, in this case, without performing any process, the process returns to step S301 (return) and waits for the arrival of the next inspection timing.

  On the other hand, when the level of the latest working pilot signal stored in the working pilot signal level storage unit 245 is less than the threshold value in step S303 (step S303: Y), there is some abnormality related to the working system. It may have occurred. Therefore, in this case, the latest level of the preliminary pilot signal stored in the preliminary pilot signal level storage unit 246 is subsequently read (step S306). Then, the voltage level is compared with the threshold value held in the threshold value holding memory 244 (step S307). As a result, if the voltage level of the preliminary pilot signal is not less than the threshold value (N), some failure has occurred in the CATV signal 205, the working transmission line 201 is disconnected, or deterioration due to secular change proceeds. There is a possibility. Therefore, in this case, a request for switching to the standby transmission path 203 is sent to the optical output signal switching unit 221 as a switching request signal 236 (step S308). Then, in order to observe the transition of the situation such as failure recovery, the process returns to step S301 (return) and waits for the arrival of the next inspection timing.

  If the level of the standby pilot signal is less than the threshold value in the comparison process in step S307 (Y), there is a possibility that some abnormality has occurred in the detection of the standby system. The abnormality may be caused by the occurrence of a failure in the working transmission line 201 and the backup transmission line 203, or the level identification unit 235 itself may be broken. Of course, some trouble may occur in the spare pilot signal. In any case, there is a possibility that the situation cannot be solved by simply switching the active transmission line 201 and the standby transmission line 203 in these cases. Therefore, in this case, the level identification unit 235 outputs an error signal (step S309) and returns the process to step S301 (return). This error signal is received by the optical output signal switching unit 221 or a circuit portion (not shown) and notified to the administrator or maintenance staff of the optical path network 200.

  In addition to the above cases, when the level of the working pilot signal is equal to or higher than the threshold value in step S303 (N), the level of the spare pilot signal may be lower than the threshold value in step S305. In this case (step S305: Y), there is a possibility that a failure on the electric signal side such as the preliminary pilot signal described above, disconnection in the standby transmission path 203, or deterioration due to secular change or the like is progressing. . Therefore, the level identification unit 235 sends a request for switching to the working transmission line 201 to the optical output signal switching unit 221 as a switching request signal 236 (step S310). Then, in order to observe the transition of the situation such as failure recovery, the process returns to step S301 (return) and waits for the arrival of the next inspection timing.

  The optical output signal switching unit 221 includes an optical device that switches between the working transmission line 201 and the standby transmission line 203. When the switch request to the backup transmission line 203 in step S308 is sent as the switch request signal 236 in a state where the working transmission line 201 is connected to the output transmission line 213, the switch to the backup transmission line 203 is performed. I do. When the standby transmission path 203 is connected to the output-side transmission path 213 and the switching request to the working transmission path 201 in step S310 is sent as the switching request signal 236, the switching to the working transmission path 201 is performed. Will do.

  As described above, according to the first embodiment of the present invention, the voltage levels of the pilot signal transmitted through the working transmission line 201 and the pilot signal transmitted through the backup transmission line 203 are detected, and the detected result is obtained. It was decided to compare with a preset threshold value as a fixed value. Then, the working or protection transmission line connected to the output-side transmission line 213 is switched based on the comparison result, so that the optical path network 200 is optical in a state where the level is lowered before the transmission signal is converted into light. Signal switching can be executed, and a highly reliable optical path network 200 can be constructed. In addition, when a failure occurs in the optical path switching device 212 or the level identification unit 235 and an abnormality is detected in the current transmission path 201 and the backup transmission path 203, an error is warned so that errors can be detected and recovered early. Can be achieved.

  <Second Embodiment of the Invention>

  Next, a second embodiment of the present invention will be described.

  FIG. 11 shows the configuration of the optical path switching apparatus according to the second embodiment of the present invention. Note that the optical path network 200 shown in FIG. 7 is also used as it is in the second embodiment. However, the optical path switching device 212 in FIG. 7 is replaced with the optical path switching device 212A in the second embodiment, and the optical path network 200 is replaced with the optical path network 200A. In FIG. 11, the same parts as those in FIG.

The optical path switching device 212A of this embodiment includes the same series circuit of the photoelectric conversion element 222 and the resistor 225 and the same series circuit of the photoelectric conversion element 223 and the resistor 229 as in the first embodiment. However, the potential change signal 226 appearing at the connection point between the photoelectric conversion element 222 and the resistor 225 is branched and input to the first working detection circuit 227 ₁ and the second working detection circuit 227 ₂ . . Similarly, the potential change signal 231 appearing at the connection point between the photoelectric conversion element 223 and the resistor 229 is branched and input to the first preliminary detection circuit 232 ₁ and the second preliminary detection circuit 232 _2. Yes.

The first working detection circuit 227 ₁ converts the optical input signal into the voltage level of the electrical signal in the wavelength band of the pilot signal transmitted through the working transmission line branch transmission line 201 ₁ . The second active detection circuit 227 ₂ converts a noise signal in a wavelength band whose frequency is shifted from the pilot signal by a predetermined amount to a voltage level. The first auxiliary detection circuit 232 ₁ converts the optical input signal into the voltage level of the electric signal in the wavelength band of the pilot signal transmitted through the auxiliary transmission line branch transmission line 203 ₁ . The second preliminary detection circuit 232 ₂ converts a noise signal in a wavelength band whose frequency is shifted by a predetermined amount from the pilot signal to a voltage level.

The detection output 401 of the _first working detection circuit 227 _{1 and} the detection output 402 of the second working detection circuit 227 ₂ are input to the working CN detection unit 403. Similarly, the detection output 411 of the _first preliminary detection circuit 232 _{1 and} the detection output 412 of the second preliminary detection circuit 232 ₂ are input to the preliminary CN detection unit 413. Working CN detection unit 403 measures C / N in the active transmission line branch transmission path 201 ₁ (Carrier to Noise Ratio). Similarly, the backup CN detection unit 413 measures C / N in the backup transmission line branch transmission line 203 ₁ .

  The CN level 404 detected by the working CN detection unit 403 is input to the CN level identification unit 405 together with the CN level 414 detected by the backup CN detection unit 413. The identification result is supplied to the optical output signal switching unit 221A as the switching request signal 236A.

  FIG. 11 described above shows a part of the optical path network 200A shown in FIG. In the entire optical path network 200A, as shown in the example of the optical path switching device 212A, the working transmission line 201 and the backup transmission line 203 exist in pairs.

  FIG. 12 shows a specific configuration of the CN level identification unit. The CN level identification unit 405 includes a CPU 241 and a main control unit 243A including a memory 242A such as a ROM (Read Only Memory) storing a control program. The main control unit 243A is connected to the following units through signal transmission means such as a bus (not shown) and performs overall control thereof.

  The threshold value holding memory 244A holds a CN level threshold value. The CN level threshold is set in advance by the administrator of the optical path network 200A shown in FIG. The working CN level storage unit 245A is an area for storing the working CN level 404 output from the working CN detection unit 403 shown in FIG. 11, and stores the latest CN level 404 by overwriting the stored contents so far. To do. Similarly, the spare CN level storage unit 246A is an area for storing the spare CN level 414 output from the spare CN detection unit 413 shown in FIG. 11, and overwrites the latest CN level 414 with the contents stored so far. And remember. Threshold comparison unit 247A compares the CN level sequentially stored in working CN level storage unit 245A or backup CN level storage unit 246A with the threshold value for the CN level held in threshold holding memory 244A. . The switch request signal output unit 248 outputs a switch request signal 236A when one of the working CN level and the backup CN level falls below the threshold value as a result of comparison by the threshold value comparing unit 247A.

  When both the working CN level and the backup CN level are lower than the threshold value, an error signal indicating the occurrence of an error may be output as in the case of the first embodiment.

  FIG. 13 shows the flow of processing of the CN level identification unit configured as described above. This will be described with reference to FIGS. In FIG. 13, the same parts as those in FIG. 10 are denoted by the same step numbers.

  The main controller 243A waits for the inspection timing of the working transmission line 201 and the standby transmission line 203 at the locations shown in FIG. 7 in the optical path network 200A to arrive (step S301). The inspection timing may be generated each time a predetermined time elapses, or the inspection timing may be generated when requested by the administrator of the optical path network 200A.

  When the inspection timing of the working transmission line 201 and the backup transmission line 203 comes (step S301: Y), the CN level identifying unit 405 reads the latest working CN level stored in the working CN level storage unit 245A (step S302A). ), The level of the threshold value stored in the threshold value holding memory 244A is compared (step S303). As a result, if the latest working CN level is not less than the threshold value (N), the latest spare CN level stored in the spare CN level storage unit 246A is read (step S304A). Then, this CN level is compared with the threshold value held in the threshold value holding memory 244A (step S305). As a result, if the latest spare CN level is not less than the threshold value (N), not only the levels of the working pilot signal and the spare pilot signal, but also the pair of working transmission line 201 and spare transmission line 203 are both normal. It turns out that it is. Therefore, in this case, without performing any process, the process returns to step S301 (return) and waits for the arrival of the next inspection timing.

  On the other hand, when the latest working CN level stored in the working CN level storage unit 245A is less than the threshold value in step S303 (step S303: Y), some abnormality related to the working system has occurred. There is a possibility. Therefore, in this case, the latest backup CN level stored in the backup CN level storage unit 246A is subsequently read (step S306A). Then, the CN level is compared with the threshold value held in the threshold value holding memory 244A (step S307). As a result, if the standby CN level is not less than the threshold value (N), some failure has occurred in the CATV signal 205, or the working transmission line 201 is broken or deteriorated due to secular change or the like. there is a possibility. Therefore, in this case, a request for switching to the backup transmission line 203 is sent to the optical output signal switching unit 221A as a switching request signal 236A (step S308). Then, in order to observe the transition of the situation such as failure recovery, the process returns to step S301 (return) and waits for the arrival of the next inspection timing.

  If the backup CN level is less than the threshold value in the comparison processing in step S307 (Y), there is a possibility that some abnormality has occurred in the detection of the backup system. The abnormality may be caused by a failure in the working transmission line 201 and the standby transmission line 203, or may be caused by a failure in the CN level identification unit 405 itself. Of course, some trouble may occur in the spare pilot signal. In any case, there is a possibility that the situation cannot be solved by simply switching the active transmission line 201 and the standby transmission line 203 in these cases. Therefore, in this case, the CN level identifying unit 405 outputs an error signal (step S309) and returns the process to step S301 (return). This error signal is received by the optical output signal switching unit 221A or a circuit portion (not shown) and notified to the administrator or maintenance staff of the optical path network 200A.

  In addition to the above cases, when the working CN level is equal to or higher than the threshold value in step S303 (N), the level of the spare pilot signal may be lower than the threshold value in step S305. In this case (step S305: Y), there is a possibility that a failure on the electric signal side such as the preliminary pilot signal described above, disconnection in the standby transmission path 203, or deterioration due to secular change or the like is progressing. . Therefore, the CN level identifying unit 405 sends a request for switching to the working transmission line 201 to the optical output signal switching unit 221 as a switching request signal 236A (step S310). Then, in order to observe the transition of the situation such as failure recovery, the process returns to step S301 (return) and waits for the arrival of the next inspection timing.

  The optical output signal switching unit 221A includes an optical device that switches between the working transmission line 201 and the standby transmission line 203. When the switch request to the backup transmission line 203 in step S308 is sent as the switch request signal 236A in a state where the working transmission line 201 is connected to the output transmission line 213, the switch to the backup transmission line 203 is performed. I do. When the standby transmission path 203 is connected to the output-side transmission path 213 and the switching request to the working transmission path 201 in step S310 is sent as the switching request signal 236A, the switching to the working transmission path 201 is performed. Will do.

  As described above, according to the second embodiment of the present invention, it is possible to switch the transmission path of an optical signal in a state where noise level is deteriorated, and to construct a highly reliable optical path network. can do. In addition, when a failure occurs in the optical path switching device 212A or the CN level identification unit 405 and an abnormality is detected in the active transmission line 201 and the standby transmission line 203, an error is warned so that early detection of the error can be performed. Recovery can be achieved.

  In the first and second embodiments described above, an example in which a pilot signal is inserted into a normal CATV signal has been shown. Of course, the present invention can be applied to transmission systems other than the CATV transmission system, and in this case, a reference signal in place of the pilot signal may be used.

10, 20, 212 Optical path switching device 11, 21 Active optical transmission line transmission means 12, 22 Backup optical transmission line transmission means 13, 23 Active pilot signal extraction means 14, 24 Backup pilot signal extraction means 15, 25 Active pilot signal voltage Conversion means 16, 26 Preliminary pilot signal voltage conversion means 17, 33 Comparison means 18, 34 Optical path selection means 27 Active noise signal extraction means 28 Preliminary noise signal extraction means 29 Active noise signal voltage conversion means 30 Preliminary noise signal voltage conversion means 31 Current CN detection means 32 Backup CN detection means 40, 50 Optical path switching method 41, 51 Active pilot signal extraction step 42, 52 Backup pilot signal extraction step 43, 53 Active pilot signal voltage conversion step 44, 54 Backup pilot signal voltage conversion step 45, 61 Comparison step 46, 62 Optical path selection step 55 Active noise signal extraction step 56 Preliminary noise signal extraction step 57 Active noise signal voltage conversion step 58 Preliminary noise signal voltage conversion step 59 Active CN detection step 60 Preliminary CN detection step 70, 80 Optical path Switching program 71, 81 Active pilot signal extraction processing 72, 82 Preliminary pilot signal extraction processing 73, 83 Active pilot signal voltage conversion processing 74, 84 Preliminary pilot signal voltage conversion processing 75, 91 Comparison processing 76, 92 Optical path selection processing 85 Current usage Noise signal extraction process 86 Preliminary noise signal extraction process 87 Active noise signal voltage conversion process 88 Preliminary noise signal voltage conversion process 89 Active CN detection process 90 Preliminary CN detection process 200, 200A Optical path network 201 Active transmission line 20 2 Active Optical Transmitter 203 Backup Transmission Line 204 Backup Optical Transmitter 205 Active CATV Signal Transmitter 206 Active Pilot Signal Transmitter 209 Backup CATV Signal Transmitter 210 Standby Pilot Signal Transmitter 213 Output Transmission Lines 221 and 221A Optical Output Signal Switching unit 222, 223 Photoelectric conversion element 226, 231 Potential change signal 227 Current detection circuit 232 Preliminary detection circuit 233, 234 Detection signal 235 Level identification unit 236 Switching request signal 241 CPU
242, 242A Memory 243, 243A Main control unit 244, 244A Threshold holding memory 245 Current pilot signal level storage unit 246 Preliminary pilot signal level storage unit 247, 247A Threshold comparison unit 401, 402, 411, 412 Detection output 404 414 CN level 405 CN level identification unit

Claims (5)

A working optical transmission line sending means for mixing a signal to be transmitted and a working pilot signal at a level serving as a reference in a specific wavelength region, and sending the mixed signal to the working optical transmission line;
A spare optical transmission line sending means for mixing the signal to be transmitted and a spare pilot signal at a level serving as a reference for a specific wavelength region, and sending the mixed signal to the spare optical transmission line;
A working pilot signal extracting means for extracting the working pilot signal from a working transmission line that has passed through the working optical transmission line sending means;
Backup pilot signal extraction means for extracting the backup pilot signal from a backup transmission path that has passed through the backup optical transmission path sending means;
Working pilot signal voltage converting means for converting the working pilot signal extracted by the working pilot signal extracting means into a voltage;
Preliminary pilot signal voltage converting means for converting the preliminary pilot signal extracted by the preliminary pilot signal extracting means into a voltage;
A working noise signal extracting means for extracting a noise signal in a wavelength band whose frequency is shifted by a predetermined amount from the working pilot signal from the working transmission line that has passed through the working optical transmission line sending means;
Preliminary noise signal extraction means for extracting a noise signal in a wavelength band whose frequency is shifted by a predetermined amount from the preliminary pilot signal from the preliminary transmission path that has passed through the preliminary optical transmission line transmission means;
A working noise signal voltage converting means for converting the working noise signal extracted by the working noise signal extracting means into a voltage;
Preliminary noise signal voltage converting means for converting the preliminary noise signal extracted by the preliminary noise signal extracting means into a voltage;
Working CN detection means for detecting a carrier to noise ratio (C / N) using the working pilot voltage converted by the working pilot signal voltage converting means and the working noise voltage converted by the working noise signal voltage converting means;
Preliminary CN detection means for detecting C / N using the preliminary pilot voltage converted by the preliminary pilot signal voltage conversion means and the preliminary noise voltage converted by the preliminary noise signal voltage conversion means;
A comparison means for comparing the current CN level detected by the current CN detection means and the backup CN level detected by the backup CN detection means with a predetermined threshold voltage;
And an optical path selecting means for selecting one transmission path as an output side transmission path from the working optical transmission path and the backup optical transmission path in accordance with the comparison result of the comparison means. Switching device. 2. The optical path switching device according to claim 1 , wherein the signal to be transmitted is an electric signal used in a service of a CATV (Cable television) optical transmission system. The optical path selection unit is configured such that when either the current CN level detected by the current CN detection unit or the backup CN level detected by the backup CN detection unit is equal to or higher than the threshold voltage, the comparison unit 2. The optical path switching apparatus according to claim 1, wherein a transmission path that is equal to or higher than the threshold voltage is selected as an output-side transmission path. A working pilot signal extraction step for extracting the working pilot signal from a working transmission line that mixes and transmits a signal to be transmitted and a working pilot signal at a reference level in a specific wavelength region;
A preliminary pilot signal extraction step for extracting the preliminary pilot signal from a preliminary transmission path for mixing and transmitting the signal to be transmitted and a preliminary pilot signal at a level serving as a reference for a specific wavelength region;
A working pilot signal voltage converting step for converting the working pilot signal extracted in the working pilot signal extracting step into a voltage;
A preliminary pilot signal voltage converting step for converting the preliminary pilot signal extracted in the preliminary pilot signal extracting step into a voltage;
A working noise signal extraction step for extracting a noise signal in a wavelength band whose frequency is shifted from the working optical transmission line by a predetermined amount from the working pilot signal;
A preliminary noise signal extraction step for extracting a noise signal in a wavelength band whose frequency is shifted by a predetermined amount from the preliminary pilot signal from the preliminary optical transmission line;
A working noise signal voltage converting step for converting the working noise signal extracted in the working noise signal extracting step into a voltage;
A preliminary noise signal voltage conversion step for converting the preliminary noise signal extracted in the preliminary noise signal extraction step into a voltage;
A working CN detecting step of detecting C / N using the working pilot voltage converted in the working pilot signal voltage converting step and the working noise voltage converted in the working noise signal voltage converting step;
A preliminary CN detection step of detecting C / N using the preliminary pilot voltage converted in the preliminary pilot signal voltage conversion step and the preliminary noise voltage converted in the preliminary noise signal voltage conversion step;
A comparison step of comparing the current CN level detected in the current CN detection step and the backup CN level detected in the backup CN detection step with a predetermined threshold voltage;
And an optical path selecting step of selecting one transmission line as an output side transmission line from the working optical transmission line and the backup optical transmission line according to the comparison result of the comparison step. Switching method. On the computer,
A working pilot signal extraction process for extracting the working pilot signal from a working transmission line that mixes and transmits a signal to be transmitted and a working pilot signal at a reference level in a specific wavelength region;
A spare pilot signal extraction process for extracting the spare pilot signal from a spare transmission line for mixing and transmitting the signal to be transmitted and a spare pilot signal at a level serving as a reference for a specific wavelength region;
A working pilot signal voltage conversion process for converting the working pilot signal extracted in the working pilot signal extraction process into a voltage;
A preliminary pilot signal voltage conversion process for converting the preliminary pilot signal extracted in the preliminary pilot signal extraction process into a voltage;
A working noise signal extraction process for extracting a noise signal in a wavelength band whose frequency is shifted by a predetermined amount from the working pilot signal from the working optical transmission line;
A preliminary noise signal extraction process for extracting a noise signal in a wavelength band whose frequency is shifted by a predetermined amount from the preliminary pilot signal from the preliminary optical transmission line;
A working noise signal voltage conversion process for converting the working noise signal extracted in the working noise signal extraction process into a voltage;
Preliminary noise signal voltage conversion processing for converting the preliminary noise signal extracted in the preliminary noise signal extraction processing into a voltage;
A working CN detection process for detecting C / N using the working pilot voltage converted by the working pilot signal voltage conversion process and the working noise voltage converted by the working noise signal voltage conversion process;
A preliminary CN detection process for detecting C / N using the preliminary pilot voltage converted by the preliminary pilot signal voltage conversion process and the preliminary noise voltage converted by the preliminary noise signal voltage conversion process;
A comparison process for comparing the current CN level detected in the current CN detection process and the backup CN level detected in the backup CN detection process with a predetermined threshold voltage;
And an optical path selecting process for selecting one of the working optical transmission line and the backup optical transmission line as an output-side transmission line in accordance with a comparison result of the comparison process. Switching program.

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